The present invention relates to an X-ray imaging system and a method thereof. More in detail it relates to an X-ray imaging system suitable for imaging a large area such as a chest, etc. and a method thereof.
A field of view of an X-ray television imaging unit consisting of an X-ray image intensifier (herein-belong abbreviated to X-ray II) and a television camera is not sufficiently great to cover the chest described above. A usual imaging system is a so constructed that X-ray, which has been transmitted through a subject, is detected by the X-ray II. However the field of view of this X-ray II, i.e. the area, of the X-ray II input screen, is limited. By present techniques the area, of the input screen, cannot be greater than 16 inches for securing a practically usable special resolution.
In order to use an imaging system having only small field of view for imaging an object greater than the field of view, heretofore several parts of the object have been imaged separately, and images thus obtained have been joined to form a synthesized image for the whole object. Such an imaging method is disclosed in Electromedica 60 (1992) No. 1, pp. 2-5. By this method the detection unit consisting of an X-ray II and a television camera is integrated in one body with an X-ray source and both are moved simultaneously and in a same direction and stopped at a plurality of predetermined positions, where imaging is effected.
However, since X-ray emitted by an X-ray source is a substantially diverging beam, inconveniences indicated in FIG. 1 can take place.
An X-ray source 3 is integrated with an X-ray detection unit 16 in one body, which is moved parallelly to a subject 17 in a dorsal position. In this case, since an X-ray beam traversing the subject 17 is a diverging beam, when the X-ray source 3 is at A, the X-ray beam passing through a position indicated by P on a surface of the abdomen passes through a position indicated by Q on a surface of the back, while when the X-ray source 3 is at B, the X-ray beam passing through a position indicated by P on the surface of the abdomen passes through a position indicated by R on the surface of the back.
Since an X-ray image on the detection unit is formed by utilizing X-rays passed through the surface of the back, in case where two images at the positions A and B thus obtained are joined, when they are joined so that the positions indicated by P on the surface of the abdomen are overlapped on each other, on the surface of the back they are joined at Q on one of the images and R on the other. Therefore the images cannot be joined precisely.
By the prior art techniques described above, in case where imaging is effected several times by using a television camera for the X-ray detection unit while moving it, it is not possible to avoid that mechanical vibration is transmitted to the television camera. As the result, stripes which are parallel to the direction of the scanning line of the television camera (horizontal direction on the image) are generated, which gives rise to a problem that image quality is worsened. This phenomenon is called microphonic noise and explanation thereof is described e.g. in "Satsuzo Kogaku (Imaging Technology) pp. 37-40" (in Japanese) as a general phenomenon for imaging using a television camera.